Tanja:
are there some substantial rumors that canon is working on such a lens?

or is it just a dream many of us share?

Canon-F1:
the 12-24 or 14-24 is a lens i desperately waiting for.

for me it does not even have to be f2.8.it only has to be very sharp from center to corners with well controlled distortions.

neuroanatomist:
Buzzzzzzzzz. Alarm goes off, dream over. :P

Seriously, I do expect they're working on a 14-24 or similar. Given that Nikon's D800 is showing the flaws in their excellent 14-24/2.8, I expect Canon is taking their time to get it right.

Canon has patented a 14-24/2.8 design.

pierceography:
I would love to see this lens released in the next year or so. But expect it to cost $2,500+. Though I would gladly pay that... <24mm presents a bit of a hole in my camera bag. Even with the Sigma 12-24mm... I'd love to have something faster with better corner performance.